In recent years, highly precise and fine image quality comparative to silver salt photography can be taken along with rapid progress of recording technology; therefore, ink-jet recording apparatuses for forming images using an ink-jet recording system have been widely used as image forming apparatuses.
Concerning these ink-jet recording apparatuses, there is a strong desire to further increase image forming speed while maintaining image quality thereof. An ink is therefore required that can be stably ejected from nozzles of recording heads without clogging the nozzles even when forming images at higher speed. An ink is also required that can promptly penetrate into recording media in order to prevent ink adhesion to discharge rollers, i.e. offset, which occurs when recording media are conveyed by discharge rollers before the ink has penetrated into the recording media.
From such a circumstance, an ink-jet recording liquid has been proposed that contains glycerin and 1,3-propanediol in a certain proportion and that allegedly provides stable ejection.
A water-based ink has also been proposed that contains a polyhydric alcohol monoalkyl ether having a vapor pressure of 0.1 mmHg or lower at 20° C. and that can allegedly effectively increase an ink penetration speed into recording media.
However, there may arise a case in the ink-jet recording liquid such that ejection of droplets of the ink-jet recording liquid cannot be maintained in a proper condition depending on the content ratio between glycerin and 1,3-propanediol when allowing recording heads filled with the ink-jet recording liquid to stand without caps for a long time. There are also problems in the ink-jet recording liquid in that it is difficult to form images with a desired image density or to maintain ejection of droplets of the ink-jet recording liquid from recording heads in a proper condition when forming images for a long time.
There is also a problem in the water-based ink described above in that viscosity of the ink and dispersion condition of pigments are considerably changed after exposing the ink to a high-temperature environment for a long time although permeability of the ink into recording media can be sufficiently enhanced.